The present invention relates to a brake fluid pressure control device of a simple structure and having both the function of antilock and traction control.
The simplest antilock device known is the so-called recirculating type which comprises a wheel brake fluid pressure control valve including a discharge valve provided in the main fluid passage extending from the master cylinder to each wheel brake, a discharged fluid reservoir for temporarily storing the brake fluid discharged from the discharge valve, and a pump for pumping the brake fluid out of the discharged fluid reservoir and returning it to the main passage. If it is desired to add the traction control function to this device, the structure of the entire device can be simplified most effectively by using the circulation pump for the antilock device as a pressure source for the traction control.
In order to employ such a structure, brake fluid has to be supplied to the inlet port of the pump. This can be done in several known ways.
These known ways are classified into two types. In one type, a supply passage is provided so as to extend directly from the reservoir for the master cylinder to the pump inlet port. In the other type, the supply passage is provided so as to branch from the main passage connecting the master cylinder outlet port to each wheel brake. Of these two types, the latter is advantageous in view of the easy mounting on a vehicle and the non-necessity of returning any redundant brake fluid to the reservoir for the master cylinder through its inlet port.
The latter method, in which the supply passage branches from the main passage, has a problem in that the amount of brake fluid that can be supplied into the pump is limited due to the resistance at the master cylinder inlet port, the resistance of the piping from the master cylinder to the brake fluid pressure control device and the flow resistance in a shutoff valve for shutting the supply passage during normal braking. Thus, there is a possibility that the brake fluid pressure may not increase sufficiently quickly when the traction control starts.